Method and apparatus for acoustic scanning using waves scattered by an acoustic grating

Abstract

An acoustic scanning apparatus is described having an acoustic grating for scattering waves into a focused beam. Surface acoustic waves are generated by a chirp signal generator and are introduced along one surface of the scanning apparatus. These waves propagate along the surface, are scattered by the acoustic grating and are thereby converted into bulk acoustic waves. The bulk acoustic waves converge into a focused beam inwardly directed at an angle to the surface acoustic waves. The focused beam scans at substantially the same speed as the surface acoustic waves traveling along the surface of the apparatus. The acoustic grating can also be used to convert bulk waves to surface acoustic waves as either a variable chirp rate generator or a variable pulse compression filter.

What is claimed is: 
     
       1. Apparatus for generating focused acoustic bulk waves, comprising: a. means for generating a chirp pulse output;   b. a solid medium for transmitting acoustic waves;   c. an array of perturbations located on one surface of the solid medium; and   d. transducer means operatively connected to the generating means and the solid medium for converting the chirp pulse from the generating means into surface acoustic waves propagating along the perturbation array surface of the solid medium, said surface acoustic waves being inwardly scattered into the solid medium by said perturbation array and converged into a focused beam of acoustic bulk waves angularly directed from the direction of propagation of the surface acoustic waves.   
     
     
       2. The apparatus of claim 1 wherein the array of perturbations includes a uniformly spaced apart plurality of parallel grooves having a spacing distance substantially equal to the wavelength of the center frequency of the chirp pulse. 
     
     
       3. The apparatus of claim 1 wherein the array of perturbations includes a uniformly spaced apart plurality of parallel strips disposed on the surface of the solid medium and having a spacing distance substantially equal to the wavelength of the center frequency of the chirp pulse. 
     
     
       4. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform spacing. 
     
     
       5. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel strips having nonuniform spacing. 
     
     
       6. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform depth. 
     
     
       7. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform width. 
     
     
       8. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel grooves having a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       9. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel strips having a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       10. The apparatus of claim 1 wherein the bulk wave beam is perpendicularly directed from the direction of propagation of the surface acoustic waves. 
     
     
       11. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel strips having nonuniform thickness. 
     
     
       12. The apparatus of claim 1 wherein the array of perturbations includes a plurality of parallel strips having nonuniform width. 
     
     
       13. The apparatus of claim 1 wherein the chirp pulse generating means includes a pulse signal generator and pulse compression filter means connected thereto and having a chirp pulse output. 
     
     
       14. Apparatus for converting focused acoustic bulk waves from an exterior source into an electrical output signal, comprising: a. a solid medium for receiving acoustic bulk waves diverging from a focus of such waves;   b. an array of perturbations located on one surface of the solid medium such that the diverging acoustic bulk waves received by the solid medium are incident on said array and are scattered thereby into surface acoustic waves propagating along the surface of the solid medium;   c. transducer means operatively connected to the solid medium for converting the surface acoustic waves propagating along the surface of the solid medium into an output chirp signal; and   d. pulse compression filter means connected to said transducer means for converting the output chirp signal obtained from the scattered acoustic waves into an electrical output signal.   
     
     
       15. The apparatus of claim 14 wherein the array of perturbations includes a uniformly spaced apart plurality of parallel grooves having a spacing distance substantially equal to the wavelength of the center frequency of the chirp signal. 
     
     
       16. The apparatus of claim 14 wherein the array of perturbations includes a uniformly spaced apart plurality of parallel strips disposed on the surface of the solid medium and having a spacing distance substantially equal to the wavelength of the center frequency of the chirp signal. 
     
     
       17. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform spacing. 
     
     
       18. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel strips having nonuniform spacing. 
     
     
       19. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform depth. 
     
     
       20. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel grooves having nonuniform width. 
     
     
       21. The apparatus of claim 14 wherein the array of perturbations include a plurality of parallel grooves having a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       22. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel strips having a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       23. The apparatus of claim 14 wherein the bulk wave beam is perpendicularly directed from the direction of propagation of the surface acoustic waves. 
     
     
       24. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel strips having nonuniform thickness. 
     
     
       25. The apparatus of claim 14 wherein the array of perturbations includes a plurality of parallel strips having nonuniform width. 
     
     
       26. Method of generating focused acoustic bulk waves, comprising the steps of: a. generating a chirp pulse with a signal generator;   b. converting the chirp pulse into surface acoustic waves propagating in a solid material; and   c. converging acoustic bulk waves into a focused beam by scattering the surface acoustic waves with an array of perturbations located on the solid material and in the path of propagation of the surface acoustic waves.   
     
     
       27. The method of claim 26 further including the step of dimensioning the array of perturbations so as to have a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       28. Method for converting focused acoustic bulk waves from an interior or exterior source into an electrical output signal, comprising the steps of: a. receiving in a solid medium acoustic bulk waves diverging from an interior or exterior focus of such waves;   b. scattering the diverging acoustic bulk waves into surface acoustic waves with an array of perturbations located on one surface of the solid medium;   c. converting the surface acoustic waves into an output chirp signal; and   d. pulse compression filtering said chirp signal obtained from the scattered acoustic waves into an electrical output signal.   
     
     
       29. The method of claim 28 further including the step of dimensioning the array of perturbations so as to have a spacing distance substantially equal to an integral multiple of the wavelength of the center frequency of the chirp pulse. 
     
     
       30. Apparatus for generating focused acoustic bulk waves, comprising: a. means for generating a chirp pulse output;   b. a solid medium for transmitting acoustic waves;   c. an array of perturbations located on one surface of the solid medium;   d. transducer means operatively connected to the generating means and the solid medium for converting the chirp pulse from the generating means into surface acoustic waves propagating along the perturbation array surface of the solid medium, said surface acoustic waves being inwardly scattered into the solid medium by said perturbation array and also converged toward a first plane located normal to the direction of propagation of the surface acoustic waves and angularly directed therefrom; and   e. means forming an acoustic lens operatively connected to said solid medium, said lens focusing the converging beam of acoustic bulk waves scattered by the array of perturbations toward a second plane located normal to said first plane and parallel to the direction of propagation of the surface acoustic waves.   
     
     
       31. The apparatus of claim 20 wherein the acoustic lens is a cylindrical lens formed in a surface of the solid medium and having an axis of symmetry parallel to the direction of propagation of the surface acoustic waves. 
     
     
       32. The apparatus of claim 31 wherein the cylindrical lens is formed in a surface of the solid medium opposite to the surface wherein the surface acoustic waves propagate. 
     
     
       33. The apparatus of claim 31 wherein the cylindrical lens is formed in the same surface of the solid medium wherein the surface acoustic waves propagate. 
     
     
       34. Apparatus for scanning an object with focused acoustic bulk waves and for recording the acoustic image of the object, comprising: a. means for generating a chirp pulse output;   b. a solid medium for transmitting acoustic waves;   c. an array of perturbations located on one surface of the transmitting medium;   d. transducer means operatively connected to the generating means and the transmitting medium for converting the chirp pulse from the generating means into surface acoustic waves propagating along the perturbation array surface of the transmitting medium, said surface acoustic waves being inwardly scattered into the transmitting medium by said perturbation array and converged into a focused beam of acoustic bulk waves angularly directed from the direction of propagation of the surface acoustic waves, said acoustic bulk waves being brought to a focus within the object and scanned across said object at substantially the same velocity as the surface acoustic waves and thereby modulated by the object;   e. a solid medium for receiving the acoustic bulk waves modulated by the object;   f. an array of perturbations located on one surface of the receiving medium such that the acoustic bulk waves received by the receiving medium are incident on said array and are scattered thereby into surface acoustic waves propagating along the surface of the receiving medium;   g. transducer means operatively connected to the receiving medium for converting the surface acoustic waves propagating along the surface of the receiving medium into an output chirp signal;   h. pulse compression filter means connected to said transducer means for converting the output chirp signal therefore into an electrical output signal; and   i. means connected to the pulse compression filter means for recording the electrical output signal therefrom and thereby the acoustic image of the object.   
     
     
       35. The apparatus of claim 34 wherein the solid medium for transmitting acoustic waves includes the solid medium for receiving acoustic waves and wherein the object is imaged by reflecting acoustic bulk waves therefrom. 
     
     
       36. The apparatus of claim 34 wherein the recording means includes an oscilloscope for visually recording the analog signal from the pulse compression filter means and further including timing means for sequencing the chirp generating means and the oscilloscope. 
     
     
       37. Apparatus for generating acoustic chirp signals, comprising: a. a solid medium for transmitting acoustic waves and having a cylindrical surface at one end thereof, said cylindrical surface having a center of curvature located within said transmitting medium;   b. transducer means for generating radially diverging acoustic bulk waves within the transmitting medium that are directed toward the cylindrical surface, said transducer means being located proximate to the transmitting medium; and   c. an array of perturbations located on the cylindrical surface of the transmitting medium and positioned in the path of propagation of the radially diverging acoustic bulk waves so as to scatter said acoustic bulk waves into surface acoustic waves, said surface acoustic waves propagate along the cylindrical surface of the transmitting medium thereby generating acoustic chirp signals.   
     
     
       38. The apparatus of claim 37 further including means for moving said transducer means with respect to the center of curvature of the cylindrical surface such that acoustic signals having a variable chirp rate are generated. 
     
     
       39. The apparatus of claim 37 further including means for reducing internal reflections of the acoustic bulk waves within the transmitting medium. 
     
     
       40. The apparatus of claim 37 further including: a. a second solid medium for transmitting acoustic waves operatively connected to the transmitting medium having the cylindrical surface, said second transmitting medium having a propagating surface in acoustic surface wave communication with the cylindrical surface of the transmitting medium such that chirp signals generated by said transmitting medium are passed to the propagating surface; and   b. a second array of perturbations located on the propagating surface of the second transmitting medium for scattering the acoustic surface waves propagating therein, said surface acoustic waves scattered by said perturbation array being inwardly focused thereby into a beam of acoustic bulk waves angularly directed from the direction of propagation of the surface acoustic waves.   
     
     
       41. Method of generating variable acoustic chirp signals; comprising the steps of: a. transmitting radially diverging acoustic bulk waves in a transmitting medium using a transducer located proximate thereto, said waves being directed toward a cylindrical surface located at one end of the transmitting medium and having a center of curvature located within the transmitting medium;   b. scattering said radially diverging acoustic bulk waves into surface acoustic waves propagating through the cylindrical surface using an array of perturbations located on said cylindrical surface; and   c. moving said transducer with respect to the center of curvature of the cylindrical surface such that variable acoustic chirp signals are generated.   
     
     
       42. Apparatus for generating acoustic chirp signals; comprising: a. a solid medium for transmitting acoustic waves and having a substantially flat surface at one end thereof;   b. transducer means for generating radially diverging acoustic bulk waves within the transmitting medium that are directed toward the substantially flat surface, said transducer means being located proximate to the transmitting medium; and   c. an array of nonuniform perturbations located on the substantially flat surface of the transmitting medium and positioned in the path of propagation of the radially diverging acoustic bulk waves so as to scatter said acoustic bulk waves into surface acoustic waves, said surface acoustic waves propagate along said flat surface of the transmitting medium thereby generating acoustic chirp signals   
     
     
       43. The apparatus of claim 42 wherein the perturbations located on the substantially flat surface are spaced to produce linearly chirped surface acoustic waves. 
     
     
       44. The apparatus of claim 42 further including: a. a second solid medium for transmitting acoustic waves operatively connected to the transmitting medium having the substantially flat surface, said second transmitting medium having a propagating surface in acoustic surface wave communication with said flat surface of the transmitting medium such that chirp signals generated by said transmitting medium are passed to the propagating surface; and   b. a second array of perturbations located on the propagating surface of the second transmitting medium for scattering the acoustic surface waves propagating therein, said surface acoustic waves being inwardly scattered by said perturbation array and converged into a focused beam of acoustic bulk waves angularly directed from the direction of propagation of the surface acoustic waves.   
     
     
       45. Apparatus for pulse compression filtering acoustic surface waves received from an exterior source, comprising: a. a solid medium for transmitting acoustic bulk waves and having a cylindrical surface at one end thereof, said cylindrical surface having a center of curvature located within the transmitting medium and forming a propagation surface for acoustic surface waves received from the exterior source;   b. an array of perturbations located on the cylindrical surface and positioned in the path of the acoustic surface waves received from the exterior source so as to scatter said acoustic surface waves into radially converging acoustic bulk waves; and   c. transducer means located proximate to the transmitting medium for receiving the radially converging acoustic bulk waves and having an output signal corresponding to the acoustic surface waves received from the exterior source after pulse compression filtering.   
     
     
       46. The apparatus of claim 45 further including means for moving said transducer means with respect to the center of curvature of the cylindrical surface such that output signals having variable pulse compression filtering are generated. 
     
     
       47. The apparatus of claim 45 further including: a. a second solid medium for receiving acoustic bulk waves from an exterior source operatively connected to the transmitting medium, said second medium having a propagating surface in acoustic surface wave communication with the cylindrical surface of the transmitting medium such that acoustic surface waves from the second receiving medium are passed to the cylindrical propagating surface; and   b. a second array of perturbations located on the propagating surface of the second receiving medium such that the acoustic bulk waves received by the second medium are incident on said array and are scattered thereby into surface acoustic waves propagating along the surface of said second receiving medium.   
     
     
       48. Method of variable pulse compression filtering acoustic surface waves received from an exterior source, comprising the steps of: a. receiving acoustic surface waves from the exterior source on a cylindrical propagating surface of a solid medium;   b. scattering the acoustic surface waves into radially converging acoustic bulk waves using an array of perturbations located on the cylindrical propagating surface;   c. receiving the acoustic bulk waves with a transducer, and   d. moving the transducer with respect to the cylindrical propagating surface such that output signals having variable pulse compression filtering are obtained from the transducer.   
     
     
       49. Apparatus for pulse compression filtering acoustic surface waves received from an exterior source, comprising: a. a solid medium for transmitting acoustic bulk waves and having a substantially flat surface at one end thereof, said flat surface forming a propagation surface for acoustic surface waves received from the exterior source;   b. an array of nonuniform perturbations located on the substantially flat surface and positioned in the path of the acoustic surface waves received from the exterior source so as to scatter said acoustic surface waves into radially converging acoustic bulk waves; and   c. transducer means located proximate to the transmitting medium for receiving the radially converging acoustic bulk waves and having an output signal corresponding to the acoustic surface waves received from the exterior source after pulse compression filtering.   
     
     
       50. The apparatus of claim 49 further including: a. a second solid medium for receiving acoustic bulk waves from an exterior source operatively connected to the transmitting medium, said second medium having a propagating surface in acoustic surface wave communication with the substantially flat surface of the transmitting medium such that acoustic surface waves from the second receiving medium are passed to the flat propagating surface; and   b. a second array of perturbations located on the propagating surface of the second receiving medium such that the acoustic bulk waves received by the second medium are incident on said array and are scattered thereby into surface acoustic waves propagating along the surface of said second receiving medium.